mother, now under intense scrutiny herself. It's part of our series "Crime and punishment." Justin Ross Harris in court, charged with murder and child cite for the death of his 22-month-old son. His behavior on the day cooper died was more than puzzling. He was having up to six different conversations with different women. And these conversations he was having with these females, were these -- of what nature were they? The most common term would be sexting. Did he ever call 911? No, he did not. Police say Harris knew exactly how dangerous leaving the child in a hot car could be after seeing this safety video on TV. If you see a child left alone in a vehicle, please call 911. And this one online. Just days before his son died. About 94 degrees. Reporter: But on June 18th 33-year-old Harris did just, that leaving his son strapped in a car seat while he went to work. Seven hours later, with temperatures approaching 90 degrees, Harris got back in the car and drove for several blocks before pulling cooper from the car. He kept saying "What have I done, what have I done." Laid him on the ground, trying to do cpr, trying to resuscitate him. Apparently the child wasn't responding P P. Harris says it was all a terrible accident, that he simply forgot to drop his child off at daycare and has pled not guilty. Ross was not aware that child was in the car. Reporter: But it's not just the father's behavior that the authorities are investigating. It's cooper's mother too. And after being told that he was deceased, did she ask to see her son or anything like that? No. Who did she ask to see? She asked to see her husband. When she was given a choice, do you want to see your child or your husband, no offense to men listening tonight, but of course a mother's going to pick her child. Of course she's going to go to her toddler. But she didn't. She went to her husband. The first thing or one of the first things she said when she went into the interrogation room was not "What happened," "What happened to cooper?" No. One of the first things if not the first was "Did you tell police too much? Did you say too much?" Yeah. That's not right. Reporter: So now the question so many are asking. Will Leanna Harris be charged as well? Damning new details emerge. Reporter: Hln's Nancy grace has been following the case closely. If she's charged, that means they were in on it together. Maybe most troubling was Leanna Harris's reaction to learning that cooper had not been dropped off at daycare. In front of several witnesses all of a sudden she states, "Ross must have left him in the car." And they're like, what? There's no other reason. No other explanation. Excuse me. "Ross must have left him in the car." And they tried to console her. They're like no, there's a thousand reasons. He could have taken him to lunch or something. We don't know yet. And she's like, no. Reporter: According to police, it wasn't the first time she had thought about a child dying in a hot car either. They say both did internet searches on that very subject. Did he discuss the issue of being afraid of children -- his child dying in a car? Yes. What did he tell you about that? He said it was a fear of his. Did he explain further things he did about this fear that he had? Yeah. He had researched or watched websites on this fear. Reporter: And in an affidavit the police allege Leanna Harris made similar statements regard researching in-car deaths and how it occurs. And when Leanna Harris arrived at the police station, she asked her husband a curious question. She had him sit down and he starts going through this and she looks at him. She's like, "Well, did you say too much?" Reporter: Detectives clearly believe this was more than just an accident. And at Harris's preliminary hearing suggested Justin and Leanna Harris both had a possible motive. Money. They had two policies on cooper. The first policy is the $2,000 policy through the Home Depot. The second one, was this something they got back in 2013? Yes. And was this something they still had at the time of the child's death? Dharkthat's correct. And how much was the policy? A $25,000 policy. This past weekend from behind bars the father, Justin Ross Harris, was explaining to his family about how to collect the money. Reporter: And then there's the way Leanna Harris has reacted since the incident. At cooper's funeral she said, "I miss him with all my heart. Would I bring him back? No. To bring him back into this broken world would be selfish." And her demeanor has been criticized as well. She didn't show any emotion when they asked her. Or actually when they notified her of cooper's death. Leanna Harris is not doing herself any favors. Looking bored and snapping gum is not going to help. I absolutely believe that prosecutors will end up charging Leanna Taylor Harris. I think that at that juncture she will be used against her husband. Is it possible that prosecutors will ultimately determine that this crime is so horrific that they're not going to cut a deal with anyone and that if they have enough evidence to go after the mother that they will say no deal with the mother, no deal with the father, we're moving forward against both of them? If I were trying this case, I would not give them a deal if I found this to be premeditated. I would try them both. For the death penalty. Authorities say Leanna Harris is not currently a suspect. And she's not been charged with any crime. The investigation continues.

This transcript has been automatically generated and may not be 100% accurate.

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